After hosting the G8 summit at Camp David on Saturday, President Barack Obama will host the NATO summit, beginning Sunday in Chicago. Mr. Obama is preparing for the NATO gathering, which has Afghanistan at the top of the agenda.

The United States last hosted a NATO summit in 1999 - two years before the al-Qaida terrorist attacks on the United States that sparked the first use of the common defense provision in the NATO Charter.

The North Atlantic Treaty Organization has expanded since then. For more than 10 years, it has been focused on Afghanistan since the 2001 attacks. Last year, it took military action in Libya in support of United Nations resolutions.

Under a timetable set two years ago, the United States and NATO are withdrawing all foreign troops from Afghanistan, about 130,000, by 2014. The Chicago summit will approve a formal shift to Afghanistan leading its own security, beginning next year.

The first meeting President Obama will have on Sunday will be with Afghan President Hamid Karzai. Mr. Obama spoke from Afghanistan earlier this month after he signed a strategic pact with the Afghan government.

"International troops will continue to train, advise and assist the Afghans and fight alongside them, when needed, but we will shift into a support role as Afghans step forward," said President Obama.

U.S. National Security Adviser Tom Donilon says the NATO summit will focus on how to sustain Afghan forces and at what levels after 2014.

"We have made really substantial progress towards burden-sharing, towards a continuing support for Afghan security but with the United States not having to bear the whole load," said Donilon.

NATO has identified a figure of $4 billion as an annual support level for Afghanistan.

Analyst Stephen Flanagan is with the Washington-based Center for Strategic and International Studies.

"Most allies have not met their pledges to the existing NATO training mission in Afghanistan over the past four years, so their willingness to do so after the ISAF [International Security Assistance Force] forces are withdrawn, when they are even more dependent on Afghan forces for their security, particularly given the incidents we have seen of late, that is a key question," said Flanagan.

NATO leaders also will discuss funding shortfalls. The United States has shouldered an increasing share of the costs of alliance operations. One of the first sessions will be about NATO capabilities - doing more with less amid budget constraints.

On missile defense, leaders will declare what is called an interim capability for the NATO missile shield for Europe that is designed to protect against launches from Iran. President Obama and NATO still face Russian objections to the program.

NATO begins its summit amid optimism for resolving tensions with Pakistan over supply routes for Afghanistan that have been closed since a cross-border incident last year that killed 24 Pakistani soldiers.

Pakistani President Asif Ali Zardari will attend the summit. National Security Adviser Tom Donilon says there are no plans for a formal bilateral meeting with President Obama, although the two leaders are likely to see each other during sessions.

The NATO talks, coming after a G8 summit in the state of Maryland, will mark another appearance on the international stage for French President Francois Hollande. During his election campaign, he pledged to withdraw French troops from Afghanistan by the end of this year.

Donilon says Mr. Hollande will need to make his "national decision" about that issue, but the United States expects it will conform to NATO commitments.

"We would look to allies to make their national decisions within the context of the overall alliance approach, which has us in ISAF until the end of 2014," he said.

Donilon calls NATO the cornerstone alliance for the United States, saying reinvigorating and revitalizing alliances has been a strategic priority for President Obama.